At present there are a number of different commercial wearing parts systems for exchangeable wearing and/or replacement parts in connection with tools of a cultivating machine, especially tines on the bucket of an earth-moving machine. Wearing parts systems of this kind usually comprise two main coupling parts in the form of a so-called “female part” and “male part”; on the one hand, a front wearing part in the form of an exchangeable tine point and, on the other hand, a rear stationary holder part which is permanently attached to the bucket. In order to achieve a dynamic, yet still reliable securement of the exchangeable tine point to the holder, the coupling parts also comprise a coupling system which is common to the parts and has a detachable locking mechanism. Each such coupling system has an extremely characteristic geometry in order thereby to try to get the wearing part of the tine to be held in place in an effective, secure and functionally reliable manner, involving only minimal wear, until the wearing part, owing to the, nevertheless, inevitable wear, has to be replaced by a new wearing part.
Coupling systems of this kind can be configured, see, for example, British patent application GB-A-2 151 207 or FIG. 7 in Swedish patent specification SE-B-469 561, such that the one, first coupling part encloses an end part, hereinafter also referred to as a beak, of the opposite, second coupling part—which latter interacts with the first coupling part—around all its outer sides like a hood, from which also the name “hood system”. One solution for the coupling system is usually obtained via one or more, in relation to the longitudinal direction of the tine, essentially transverse locking devices, for example a wedge, a slotted pipe, etc., which are introduced through purpose-made locking device openings made through the hood and the beak. These locking devices can be placed centrally through the tine or on one or both sides of the tine. The free outer circumferential edge of the hood, hereinafter referred to as the tine collar, is usually corresponded to by an edge, opposite the tine collar and interacting with the tine collar, disposed on the holder, hereinafter referred to as the beak collar.
Known commercial hood systems of this kind are very often configured to absorb loads (F) which act parallel or approximately parallel with the line of symmetry of the coupling geometry in the Y-direction toward the cutting edge of the tine point, i.e. essentially along a plane extending in the longitudinal direction of the tine, see FIG. 1, via one or more, specially configured and mutually interacting contact zones, which are disposed at a certain angle to the said line of symmetry and plane, hereinafter referred to as the longitudinal axis, and horizontal plane or YZ-plane. Each such contact zone comprises at least two mutually opposite and interacting contact faces, at least one of which is disposed in the first coupling part, whilst the second is disposed in the second coupling part. When these contact faces are placed substantially perpendicular to the said longitudinal line of symmetry Y, i.e. essentially in the cross-vertical plane (XZ), further threading is stopped dead by the tooth on the holder, so that these surfaces are also hereinafter referred to as stop faces. Another way is to arrange the contact faces at a certain inclination to the different planes, whereby the load is absorbed by the friction forces which are attained owing to the wedging effect between the surfaces.
It will be appreciated, however, that, in the use of the tool, not only are loads formed which are parallel with the longitudinal plane of symmetry, in the Y-direction, of the coupling geometry, but also loads which deviate from the Y-direction. Essentially each load (F) therefore comprises an axial force component Fy, which is formed parallel with the longitudinal direction of symmetry Y of the coupling geometry and acts perpendicularly to a cross-vertical plane in the X-direction, hereinafter also referred to as the XZ-plane, on the one hand a lateral transverse force component in the Z-direction, Fz, which acts perpendicularly to the longitudinal vertical plane of the coupling geometry, hereinafter referred to as the side plane or the XY-plane, and, on the other hand, a further transverse force component Fx, which acts in the X-direction perpendicularly to the YZ-plane of the coupling geometry, i.e. the said horizontal plane.
The designations which are used below, such as vertical faces, side faces, horizontal faces, etc. can consequently be derived from the above-stated definitions for the said forces and planes.
Those loads against the tine point which give rise to transverse forces, i.e. the two latter transverse component forces Fx and Fz, are partially absorbed by means of similar contact zones comprising vertical and lateral contact faces arranged at different angles to the directions of action.
The component forces Fx, Fy and Fz can also, as a result of their leverage ratio, give rise to troublesome torque loads, which have to be absorbed via double contact zones disposed on either side of the axis about which the rotation occurs. Each of these contact zones consists, in the same way as previously, of at least two interacting contact faces. For example, the torque load which is caused by the transverse component force Fx is absorbed via at least one front and one rear contact zone relative to the Y-direction, which contact zones expediently are disposed essentially parallel with the Y-line of symmetry on either side of the locking device and on their respective opposite coupling part.
For example, in the coupling systems which are known by virtue of the said specifications SE-B-469 561 and GB-A-2 151 207, the holder part and the tine part respectively comprise, viewed in a vertical longitudinal section (XY), V-shaped concave and convex stop faces respectively, tapered toward the tine cutting edge, which stop faces mutually interact and absorb the axial forces Fy, but also absorb torque loads caused by vertical forces Fx about the Z-axis. Longitudinal ridges with corresponding grooves are provided in order to absorb the lateral forces Fz. Over and above this, the collars of the holder part and tine part comprise V-shaped and rectangular protections and recesses respectively, which are complementary to each other and which also, for their part, act as stop faces, i.e. they are in contact with each other along their vertical end faces after the coupling parts have been brought together into their common end position. These projections and recesses respectively are herein meant to eliminate the mobility between the holder part and the tine part which is a consequence of inevitable production tolerances, but they will also absorb torque loads, which can lead to the emergence of undesirable leverage ratios after a certain period of asymmetrical wear.
During operation, in fact, all the integral contact faces, inclusive of the stop faces, will be sheared, worn and deformed to a varying extent during irregular dynamic motion between wearing part, holder part and locking device. Moreover, both the tine part and the holder part will suffer essentially equal wear, with the result that both of them have to be replaced once the wear has reached its maximum level. This is very costly, of course, and since each holder part, moreover, is welded to the bucket, the down time is far longer than with a rapid replacement of just the wearing part.
It is therefore desirable to achieve a coupling system which allows essentially only the wearing part to be subjected to serious wear and tear, whilst the holder part and the locking device are substantially excluded from at least external wear, and in which inevitable wear between the contact faces of the parts, as far as possible, only occurs in respect of predetermined and specially purpose-made surfaces.
A further and very serious problem with the abovementioned coupling systems is that the locking device risks being cut off by the shearing forces which are generated, on the one hand, when the tine part and the holder part are displaced horizontally toward each other owing to continuous wearing down of the angled stop faces and of the stop faces on the collars, and, on the other hand, when the coupling system is subjected to unfavourable rotational loads about an unforeseen contact, newly arisen because of the wear, between the collars of the wearing parts system. In order to avoid this happening, a stop zone is provided which has a butting effect right from the point of coupling, by which arrangement the vertical end faces of the two collar parts, at least initially, are not in mutual contact. An example of this is shown in American patent specification U.S. Pat. No. 2,689,419, in which a front, essentially vertical stop face has been disposed at the front edge of the holder beak for interaction with a corresponding inner stop face inside the hollow of the wearing part.
As the wear increases on the original vertical stop faces designed for wear, a second and undesirable secondary contact zone will form, however, between the rear edge of the tine collar of the wearing part and the front edge of the collar of the holder, i.e. a secondary stop zone is formed around the tine collar and the holder collar in the vertical plane XZ of the respective collar, which edges/vertical planes do not initially meet and which secondary stop zone, moreover, will gradually grow.
If the tine is now subjected to a transverse force, Fx and Fz, acting toward the line of symmetry Y of the coupling geometry, at the tine point, the rotary motions in the coupling system will increasingly depend on the positions of the secondary, unfavourable stop faces. The new stop faces on the collar, in combination with the locking device, therefore replace the previous front and rear horizontal contact faces and the corresponding front and rear vertical side contact faces along essentially the YZ and XY-plane respectively, which contact faces were intended to lift the transverse forces Fx and Fz respectively which were so unfavourable to the locking mechanism. A torque leverage which is very detrimental to the strength will in this case be obtained for the majority of load cases, which leverage will give rise to the shearing forces which will cut off the locking device.
In the coupling system according to U.S. Pat. No. 2,689,419, the locking wedge is at its weakest at the tapered end of the locking wedge, precisely where the said shearing forces are likely to be greatest, i.e. on the friction surfaces between the wearing part and the holder part, both owing to the leverage ratios of the said loads and owing to the fact that the play between the collars is equally great all the way round, with the result that the undesirable secondary contact zone will very easily be formed such that the leverage ratio is obtained which is most unfavourable to the construction.
Further, when an extensive wear has occurred on the contact and stop faces, the remaining material between the locking device openings in the hood and the rear edge of the wearing part, and the material between the horizontal friction surfaces of the holder beak and the locking device opening through the beak will have been weakened so much that cracks are formed, after which the coupling is broken apart. In order to try to avoid this process, the thickness of the material on the sides of the wearing part and around its locking device opening has been increased in the Z-direction, at the same time as the tine collar of the wearing part has acquired a reinforcement in the form of a projection rearward toward the holder part, so that the actual locking device opening has been able to be moved rearward. The material thickness of the beak has also thereby increased at the level of its locking device opening. This solution adds to the cost and complexity of production, at the same time as the increased material thickness of the beak also means a higher profile of the tine in the portion over the beak, which is unfortunate from the penetration aspect. Moreover, the so-called exchange will be worse owing to the material which has necessarily been applied rearward to the wearing part of the known tine. To obtain as large an exchange as possible is fundamental to the design of a new tine. In order to create an optimal tine, the part which is left when the tine is worn out should be as light as possible in terms of weight. Since the price of wearing parts can often be approximated in Kr./kg. and since the overwhelming part of the wear occurs on the tine point, i.e. that part of the wearing part which is in front of the inner hollow, a tine should have the smallest possible share of its weight behind the tine point defined according to the above.
Further essential objects of the present invention are therefore to prevent the described secondary contact zone between the tine and holder collars from being able to be formed by chance and at least substantially to reduce the risk of the secondary contact zone being able to give rise to shearing forces which are unfavourable to the locking mechanism.
Because of the tapered shape of the holder beak in the direction of the front edge, previously known coupling systems have shown a tendency to allow the tine part to move forward when vertical load is applied to the tine point, i.e. to allow the tine part to slide off along the holder part performing a ski jump, thereby subjecting the locking device to undesirable stress. It is therefore a requirement that a wearing parts system construction shall be attainable which eliminates or at least minimizes this tendency.
Locking Mechanism—General:
Present-day locking devices are essentially constituted by two different types, on the one hand, solid and, on the other hand, elastically working locking devices.
The solid locking devices have a rigid lock body, which, for example, can be straight, such as bar-shaped, or more wedge-shaped. The elastic locking devices usually comprise a somewhat elastic element, for example a spring or an elastomer, which is compressed in connection with each fitting and removal of the locking device, by which element the tine part is forced up onto the holder part by the force created by a pretensioning of the elastic element, at the same time as the locking device is prevented from moving out of its position. Locking devices can also be classified according to how the locking mechanism is placed, i.e. the extent to which the locking device is intended to be fitted vertically or horizontally in relation to the coupling geometry of the tine. For both types there are both advantages and disadvantages, but since today's customers often choose the vertical locking devices because of their greater user-friendliness, i.e. much simpler fitting and removal, and, to a certain extent, because the vertical locking devices enable the tine to be given a lower profile with accompanying higher penetrativeness, it remains to try to reduce or eliminate the disadvantages of the vertical locking devices. These disadvantages are constituted, above all, by the risk that the locking device, when dynamic vertical load is applied to the tine point, will “work itself out” of the locking device opening such that the tine point falls off, and by the fact that the said dynamic vertical loads subject the locking mechanism to much more serious shearing forces in the case of vertical placement than in the case of a horizontal placement.
Three-Section Locking Mechanism:
Known locking devices have normally to be removed by means of powerful hammer blows, which means that the more solid types quickly become unusable owing to the wear and the deformation which occurs on the lock body and along the locking device opening. The wedge-shaped type, though simple to fit and remove, also has a greater tendency to come loose owing to the vibrations and dynamic stresses which are generated during normal operation.
In the case of elastic locking devices, the said pretensioning will accelerate the ageing of the elastic element and thereby reduce the maximum working life of the locking mechanism. When the rubber or the spring ages, the pretensioning required for the locking device to remain seated in the opening despite the said problems with vibrations, unfavourable tolerance levels, wear and other stresses on the contact faces, etc., all of which adversely affect the horizontal motions of the wearing part on the holder part, will in fact steadily decrease until the locking device, quite simply, can fall out by itself. In order for the locking mechanism always to have contact with tine and holder and thereby pretension the tine up onto the holder, a relatively long pretensioning distance is required, i.e. the distance by which the elastic element is compressed and expanded. The elastic element must also be able to perform a large number of changing compression cycles over a long period without the locking element being prone to overcompression, yet must still be able to maintain its functioning essentially as before, thereby raising the quality requirements and hence the price. Overcompression is often what first limits the working life of the locking mechanism, with the result that the dimensions for the elastomers are often increased in order thereby to compensate for the overcompression problems.
One requirement is therefore to be able to produce a locking mechanism which preferably never needs to be compressed more than the compression which is required in order to achieve the pretensioning necessary to the operation or which essentially only needs to be compressed a little further in connection with the actual fitting and removal of the locking device. A further requirement is for the locking device to be able to be introduced to approximately half its length before a hammer-fitting becomes necessary. This yields the advantage that the locking device does not need to be stabilized manually as it is actually being hammered down.
A solution to the above-stated problems which has previously been adopted in connection with elastic locking devices has been for the locking device and the receiving locking device opening to have been configured such that the various plates of the locking device, i.e. the movable engagement part(s) which is/are fixed to or controlled by the elastic element, after an initial extra compression of the element during the actual introduction of the locking device through the locking device opening in the hood, reach an extra inner cavity inside the locking device opening through the beak, which cavity is somewhat more spacious than the actual hole through the hood. The engagement parts of the locking device can now be inserted into this cavity via a slight expansion of the elastic element. In this case, a locking device situated in the cavity does not, therefore, always need to be as pretensioned as in the actual initial introduction in order to achieve a necessary locking. However, elastic locking devices of this kind, introduced into an inner cavity, are difficult to remove, since the compression which is necessary for the removal of the locking device becomes more difficult to achieve. The above-stated method of attempting to remove the locking device by hammer blows often results, if a spring is used, in the said spring being broken off. If a body which is elastic in all directions is used, a rebound is instead obtained, which is caused by the elastic element not being able to expand in another direction upon impact, with the result that the compression and the expansion occur in substantially the same direction as the hammer blows.
Notch for Locking Mechanism:
A known solution is to use an elastic rubber core which is thinner in the middle so as to compensate for the expansion of the rubber when compressed or to make the cross section of the locking device opening somewhat larger than that of the locking device, i.e. to provide extra spaces which are kept empty purely for the expansion of the rubber to allow removal of the locking device, works only if these spaces are not filled with dirt, “Dirt”, i.e. snow, clay, soil, etc. will, in fact, quickly penetrate into and fill this extra space. Should “the dirt”, moreover, dry or freeze into a compact body, the replacement of tines is made yet more difficult.
These locking devices, too, are therefore very difficult to undo after a certain period of use. Should the extra space along the hole be made sufficiently large or continuous to allow removal of the dirt from the outside, then the disadvantage is instead obtained that the strength of the tine naturally declines when the thickness of the material decreases, without an actual solution to the dirt-sticking problem.
It is therefore a high requirement to be able to produce a considerably improved locking device which has the advantages of the simple fitting and removal of the wedge shape, the advantageous springing of the elastic locking device, without its pretensioning leading to premature ageing of the rubber, and the characteristic that “dirt” shall not be able to accumulate or, at least, shall not be able to prevent the elastic part of the locking device from expanding sufficiently for the locking device to be easily detachable, even out of an inner, empty cavity intended for the locking device.
The Pin and the Shearing Zone Relocation:
In the sliding zone between the tine part and the holder part, see, for example, U.S. Pat. No. 2,689,419, the details 58, 59 in FIG. 15, a shearing force critical to the durability of the locking device is generated, which is caused by horizontal motions between the coupling parts. The said sliding zone has, moreover, the worst leverage ratio of all hood-type wearing parts systems, i.e. the longest leverage from the Y-line of symmetry, with the result that the shearing forces caused by occurring torque loads are most intensive in this section. These shearing forces risk cutting off the locking device, with the result that an unbroken cross section through only the homogeneous part of the lock body is desirable. In the cross section in which the lock body is weakened by a hollow for an elastomer, no or minimal shearing forces should therefore be generated. At the same time, with this type of locking device, the securing plate of the locking device should be disposed no higher than level with the inner side of the tine part inside the hood, i.e. “the hood roof”, in order to be able to secure the locking device in its position, whereby the position of the top edge of the said hollow for the elastomer is also essentially determined. Having the locking device carry out the securement in the holder part instead of against the hood roof leads to undesirable loads being transferred via the locking device to the holder part. The optimal load case is, in fact, that in which all dynamic loads are transferred directly from the tine part to the holder part and never via the locking device. The optimal use of the locking device is solely to prevent the wearing part from falling off when the tool is lifted from the ground surface and to hold the special contact faces of the coupling parts in mutual contact without play. Further, a placement of the securing plate against the hood roof leads instead to the elastomer hollow coming so “high up” that the said unbroken cross section cannot be obtained. Yet another requirement is therefore to produce a locking device which resolves this conflict of interests.